To date there is little evidence on the effect of property-liability (P-L) insurer's business strategy and organizational structure change on their frontier efficiency performance and productivity change. This issue is important since traditional theory assumes firms that minimizes cost and maximizes profit with more efficient strategy will survive in the long run. The main goal of this dissertation is to examine the efficiency performance in the U.S. P-L insurance industry using frontier efficiency and productivity methods. This dissertation consists of three essays on the efficiency studies. The first essay uses the data envelopment analysis to examine the efficiency performance and economies of scope for nonspecialists and specialists in the U.S. P-L insurance industry. The empirical evidence suggests that nonspecialists (specialists) dominate specialists (nonspecialists) in producing nonspecialists (specialists) input–output vectors and provide evidence for the coexistence of economies of scope and diseconomies of scope in the U.S. P-L insurance industry. Our second essay uses the stochastic frontier analysis to examine whether nonspecialized strategy dominates specialized strategy in the U.S. P-L insurance industry. The empirical evidence supports that both the nonspecialized hypothesis and the specialized hypothesis hold for different types of P-L insurers. Our third essay investigates whether the conversion of U.S. P-L insurers improves their efficiency performance before and after conversion. The empirical evidences of the value-added approach and the financial intermediary approach indicate that converting insurers experience improvement in their efficiency relative to mutual counter samples after the conversion, supporting the efficiency hypothesis proposed by Mayers and Smith (1986). Overall, the evidence of this dissertation shows that P-L insurer's diversification strategy and organizational structure change has significant impact on their frontier efficiency performance and productivity change.